Book/Report

FZJ-2019-00808

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Atomare Diffusionsprozesse auf Pt(111) untersucht mit temperaturvariabler Rastertunnelmikroskopie

Bott, M. (Corresponding author)FZJ*

1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21413

Report No.: Juel-3133

Abstract: Pt-adatom migration and nucleation on the Pt(111) surface have been investigated by variable temperature $\underline{S}$canning $\underline{T}$unneling $\underline{M}$icroscopy (STM). For this purpose a variable temperature STM operating in $\underline{U}$ltra $\underline{H}$igh $\underline{V}$acuum (UHV), in the temperature range 20K to 700K has been developped. New methods to improve vibration isolation of the STM from the surrounding area and especially from the vibrating kryostat are introduced. The improved performance of the STM allows now to routinely image the dense packed Pt(111) surface in atomic resolution down to the lowest temperatures. The main result of the investigations is the development and application of a new method for the determination of adatom diffusion parameters. The method is based on a combination of STM measurements and kinetic Monte Carlo simulations. Small amounts of Pt adatoms were deposited on the Pt(111) surface at various fixed temperatures and imaged at 20 K. As long as the deposition temperature is low enough, the Pt adatoms are immobile and can be imaged individually. Using this capability of the STM the onset of the diffusion within "experimental time", i.e. time of deposition and held on temperature, has been monitored. The island density plotted versus temperature is therefore constant for temperatures below the onset temperature and decreases rapidly above this temperature. This feature can be simulated by kinetic Monte Carlo simulations. Due to the low temperature the diffusion on terraces is the only activated process.Therefore there are only two free parameters in the simulation: attempt frequency and activation barrier for diffusion. These are thus unequovocally determined by fitting the right onset temperature and the correct slope of island density curve. With this combination of simulation and STM measurements an attempt frequency of 5$\cdot$10$^{12}$ Hz and an activation energy E$_{d}$ = O,26eV is determined. In order to test the result two independent experiments were performed: the island density versus coverage at a fixed temperature of T = 180K and the island density versus temperature at saturated island density from 150K to 265K. In both cases the determined pair of parameters of the Monte Carlo simulation was confirmed. The new method of determination of adatom diffusion parameters is completely independent from nucleation theory. This allowed to use the new method to test the rate equation approach of nucleation theory. One main application of nucleation theory is the determination of the diffusion coefficient D, i.e. attempt frequency and activation barrier, by [...]

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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